Isolation of large numbers of mesenchymal stem cells from the washings of bone marrow collection bags: characterization of fresh mesenchymal stem cells.

Background: Bone marrow (BM) is an excellent source of mesenchymal stem cells (MSC) which can be expanded in vitro for further use. However, large volumes of BM specimens are not routinely available. We hypothesized that the normally discarded BM collection kits might be a convenient source of large numbers of MSC.

Methods: Marrow specimens were isolated from used Fenwal collection kits. Purified mononuclear cells (MNC) were screened by multiparameter flow cytometry to identify MSC, which were later expanded by in vitro culture. Immunophenotyping and differentiation assays were performed initially and at subculture. Both fresh and frozen BM were tested.

Results: An average of 9.62E+08 MNC were collected. In this, a cell population was identified that was CD44+, CD73+, CD90+ and CD105+, but negative for hematopoietic markers. This population represented on average 0.015% of the total BM MNC fraction, or on average 1 in 6,666 MNC. The population was considered to be MSC based on its immunophenotype profile, suppressive ability in mixed lymphocyte cultures, morphology, and ability to differentiate into bone and fat cells.

Conclusions: This study demonstrates that large numbers of MSC can be obtained from the normally discarded collection devices following harvest of BM for clinical transplant. This novel method offers potential for obtaining large numbers of MSC for potential therapeutic or investigational purposes following their in vitro expansion.